Organic compounds

ABSTRACT

Intermediates useful in the preparation of compounds having a penam or cephem ring structure, particularly penicillins and cephalosporins, and their preparation.

This is a division of Ser. No. 566,695 filed Apr. 10, 1975 now U.S. Pat.No. 3,996,235, issued Dec. 7, 1976, which is a divisional of Ser. No.443,724, filed Feb. 19, 1974, now U.S. Pat. No. 3,936,446, issued Feb.3, 1976.

This invention relates to intermediates useful in the preparation ofcompounds having the penam or cephem ring structure particularlypenicillin and cephalosporin compounds which have antibacterial activity

According to the present invention there is provided a compound offormula (I) ##STR1## wherein n is 0 or 1 and Z is a divalent radical offormula (II), (III) or (IV) ##STR2## wherein R is hydrogen an acetoxygroup, a pyridinium group or a heterocyclic thio group, and X is acarboxylic group or a salt or ester derivative thereof or X and R takentogether in formula (III) or (IV) represent the divalent radical##STR3##

When X is an esterified carboxylic acid group, the most versatile estersare those which can readily be hydrolysed to the parent acid. Examplesof suitable esters include the benzyl, para-methoxybenzyl,2,2,2-trichloroethyl, and tert-butyl esters. Other suitable estersinclude the acyloxymethyl esters such as acetoxymethyl andpivaloyloxymethyl esters as well as "lactone" esters of structure (V)##STR4## wherein Z¹ is a divalent radical such as 1,2-phenylene or4,5-dimethoxyphenyl-1,2-ene-radical.

The CN--C bond in compounds (I) may be either cis or trans with respectto the bridgehead hydrogen, and, as will be apparent later, mixtures ofthe cis and trans isomers are generally formed when preparing compounds(I).

When R is a heterocyclic thio group, particular examples include thefollowing: ##STR5## although many other examples of heterocyclic thiogroups are known (see for example those listed in British Pat. Spec. No.1,328,340)

Compounds of formula (I) are prepared by reacting a compound of formula(VI) ##STR6## wherein n and Z are as defined in formula (I) withphosgene in the presence of an acid acceptor. Preferably the acidacceptor is a tertiary amine such as N-methylmorpholine. The compound offormula (VI) used as starting material may be prepared by N-acylatingthe 6- or 7- amino compound with an N-acylating derivative of formicacid e.g. formicacetic anhydride or the intermediate formed when acarbodiimide coupling agent is used with formicacid. The above reactionis most preferably carried out using a compound (VI) in which the groupX is an esterified carboxylic acid group, since this gives a cleanerreaction. If desired, the ester group may then be hydrolysed to give theparent acid or salt. When cephem structures (I) are to be prepared, itmay be preferable to carry out the phosgene reaction using a compound(VI) wherein R is not the ultimately desired group, and thereafterintroduce the desired group e.g. by nucleophilic displacement. Thus thephosgene reaction might be carried out using the corresponding 3-acetoxycompound which is later displaced by a heterocyclic thiol.

In general, mixtures of the α- and β- isomers of the isocyano compound(I) are obtained after the phosgene reaction, the ratio of one isomer tothe other being dependant on reaction conditions such as solvent,temperature and time. Usually separation of isomers is not necessarysince the isomeric mixture can be used as the intermediate in the sameway as the pure isomers.

The value of compounds (I) derives from their use in the preparation ofthe corresponding 6- or 7- substituted compound (VII) ##STR7## wherein nand Z are as defined in formula (I) and R¹ is a group derived from anelectrophile e.g. hydroxy alkyl, alkoxycarbonylalkyl,aralkoxycarbonylalkyl, aralkyl, alkylthio and the like. It is known thatpenicillins and cephalosporins having both an acylamino substituent anda second substituent at position 6- or 7- respectively are of value asantibacterial agents (of Belgian Pat. No. 768,528). The isocyano groupof compounds (VII) above may be converted to a free amino group byreaction with an acid which does not cleave the β-lactam ring of thepenam or cephem (e.g. arylsulphonic acids such as p-toluenesulphonicacid). The free amino group may then be acylated by any of theN-acylation procedures known for semisynthetic penicillins andcephalosporins. In addition, the substituent R¹ in compounds (VII) maybe modified further either before or after conversion of the isocyanogroup to an amino or acylamino group. Thus the versatility of theintermediate compounds (I) is clear, and specific examples of their useare given later in this specification.

The following Examples 1 to 9 illustrate the preparation ofrepresentative compounds of formula (I), whilst the remaining Examplesillustrate the use of such compounds in the preparation of penam andcephem structures having an electrophile - derived substituent atposition 6- or 7-.

EXAMPLE 1 Benzyl 6-Isacyanopenicillianate

A solution of benzyl 6β-formylaminopenicillanate (4g) in dry methylenechloride (40 ml) was treated with N-methylmorpholine (3.3 ml) and thenat -50° C. with a methylene chloride solution of phosgene (1.2 g). Thereaction was exothermic. After 30 minutes at -40° C. ice-water was addedand the organic phase was washed with water and dried. Evaporation gavecrude benzyl 6-isocyanopenicillanate. Column chromatography on silicagel using 30% v/v ethyl acetate in light petrol (60°-80° C.) gave asemisolid mixture of the 6α- and 6β- epimers (ratio 55:45) (1.2 g), fromwhich the 6α- isomer was obtained by fractional crystallisation fromether, m.p. 87°-89° C. ν_(N) C^(CHCl).sbsp.3 2140 cm⁻ ¹.

EXAMPLE 2

Following the same procedure as in Example 1, the phthalidyl ester of6β-formylaminopenicillanic acid was converted to phthalidyl6-isocyanopenicillanate. ν_(max) (CHCl₃) 2120, 1790, 1770 (shoulder) cm⁻¹

EXAMPLE 3

Following the same procedure as in Example 1, the t-butyl ester of7β-formylaminocephalosporinate was converted to t-butyl7β-isocyanocephalosporinate as a chromatographically homogeneous syrupν_(N) C^(CHCl).sbsp.3 2140 cm⁻ ¹.

EXAMPLE 4

A solution of methyl 7β -formylaminodesacetoxycephalosporanate (1.02 g)in methylene chloride (25 mls) was treated with N-methylmorpholine (1.1ml) and then at -40° C. to -50° C. with a 2 M solution of phosgene inmethylene chloride (2.5 mls). After 1 hour, water was added and theorganic phase separated. The latter was washed with aqueous sodiumbicarbonate solution then with water, and dried and evaporated to givemethyl- 7β-isocyanodesacetoxycephalosporanate. Chromatography on silicagel gave the product as an oil ν_(max) (CH Cl₃) 2110 1785, 1720 cm⁻ ¹.

EXAMPLE 5

A solution of methyl 7β-formylamino-3-(2¹ -methyl-1¹, 3¹, 4¹-thiadiazol-5¹ -yl)thiomethylceph-3-em-4-carboxylate (0.81 g) inmethylene chloride (15 mls) was treated with N-methylmorphine (0.56 ml)and then at -50° C. to -60° C. with a 2 M solution of phosgene inmethylene chloride (1.2 mls). After 1 hour at -40° C. and 0.5 hour at20° C. ice-water was added and the organic layer separated. The latterwas washed with aqueous sodium bicarbonate solution then water, anddried and evaporated. Chromatography on silica gave methyl7β-isocyano-3-(2¹ -methyl-1¹,3¹,4.sup. 1 -thiadazol-5¹-yl)-thiomethylceph-3-em-4-carboxylate. (0.16 g) ν_(max) (CH Cl₃) 2110,1780, 1720 cm⁻ ¹.

EXAMPLE 6

By the general procedure of Example 1, using as starting material benzyl6β-formylaminopenicillanate sulphoxide, benzyl 6-isocyanopenicillanatesulphoxide is prepared.

EXAMPLE 7

By the general procedure of Example 4 using as starting material methyl7β-formylaminodesacetoxycephalosporanate, methyl7β-formylaminodesacetoxycephalosporanate sulphoxide is prepared.

EXAMPLE 8

By the general procedure of Example 4 using as starting material methyl7β-formylamino-3-methylceph-2-em-4-carboxylate, methyl 7β-isocyano-3-methylceph-2-em-4-carboxylate is prepared.

EXAMPLE 9

Catalytic hydrogenation of the product of Example 1 using Raney Nickleproduces 6-isocyanopenicillanic acid.

EXAMPLE 10 Benzyl 6α-[1'-hydroxyisopropyl]-6β-isocyanopenicillanate

A mixture of benzyl 6α- and 6β-isocyanopenicillanate (0.71 g ) dryacetone (5 ml.) and powdered potassium carbonate (0.31 g.) was stirredat 20° C. with monitoring of the reaction by thin layer chromatographyWhen all starting material had disappeared (2 hours) ice-water was addedand the acetone was removed at 20° C. Extraction of the aqueous residuewith ether was followed by washing the extracts with water drying andevaporation to yield the crude 6α-[1'-hydroxyisopropyl] derivative.Purification by column chromatography on silica gel led to the productas a syrup (0.5 g.); ν_(N) C^(CHCl).sbsp.3 2130 cm⁻ ¹.

EXAMPLE 11 Benzyl 6α-methoxycarbonylmethyl-6β-isocyanopenicillanate

When a mixture of benzyl 6α- and 6β-isocyanopenicillanate epimers,dimethylformamide (3 ml.) and powdered potassium carbonate (0.24 g) werestirred together in the presence of methyl bromacetate (0.16 ml.) for 3hours in an ice-bath, work up and chromatography as described in Example10 led to the benzyl 6α-methoxycarbonylmethyl-isocyanopenicillanate as aclear colourless syrup, (0.3 g.); ν_(max) ^(CHCl).sbsp.3 2130, 1790,1740 cm⁻ ¹.

EXAMPLE 12 Benzyl 6α-benzyloxycarbonylethyl-6β-isocyanopenicillanate

A mixture of benzyl 6α- and 6β-isocyanopenicillanate epimers (3.8 g) indry dimethylformamide (15 ml.) was stirred at 20° C. with powderedpotassium carbonate (1.7 g) and benzyl acrylate (2.5 g.) for 11/2 hours.Addition of ice-water was followed by extraction of the precipitated oilinto ethyl acetate. The extracts were washed with water dried andevaporated. Column chromatography of the residue on silica gel using 30%ethyl acetate in petrol as eluent provided benzyl6α-benzyloxycarbonylethyl-6β-isocyanopenicillanate as a syrup (2.8 g.);ν_(N) C^(CHCl).sbsp.3 2120 cm⁻ ¹.

EXAMPLE 13 Benzyl 6α-benzyl-6β-isocyanopenicillanate

A mixture benzyl 6α- and 6β-isocyanopenicillanate epimers (1.0 g.)dimethylformamide (3.5 ml.), potassium carbonate (0.47 g.) and benzylbromide (0.43 ml.) were stirred together for 21/2 hours in an ice-bath.The reaction was worked up as in Example 10 and column chromatographygave benzyl 6α-benzyl-6β-isocyanopenicillanate (0.24 g.), m.p. 105°-107°C.

EXAMPLE 14 t-Butyl 7α-benzyloxycarbonylethyl-7β-isocyanocephalosporanate

t-Butyl 6β-isocyanocephalosporanate was reacted as described in Example12, chromatography of the crude product led to t-butyl7α-benzyloxycarbonylethyl-7β-isocyanocepholosporanate as a colourlesssyrup; ν_(max) ^(CHCl).sbsp.3 2120, 1795, 1735 cm⁻ ¹.

EXAMPLE 15 Benzyl 6α-benzoylmethyl-6β-isocyanopenicillanate

A solution of benzyl 6-isocyanopenicillanate (mixed C6-epimers) (1.43 g)in dimethylformamide containing anhydrous potassium carbonate (0.63 g)and phenacylbromide (0.9 g) was stirred for 4 hours at 5° C. Work up andchromatography provided the desired compound as an oil (0.35 g.)

ν_(max) (CHCl₃): 2120, 1795, 1740, 1680 cm⁻ ¹.

EXAMPLE 16 t-butyl 7α-isocyano-7β-methylthiocephalosporante

A mixture of 7β-isocyanocephalosporanate (1.7 g), potassium carbonate(0.7 g), methylmethoxycarbonyldisulphide (0.7 g.) and dimethylformamide(10 mls.) was stirred for 21/4 hours at 5°-10° C. After addition ofwater, the neutral product was isolated from ethylacetate. On the basisof spectral evidence this contained the desired isocyanide: ν_(max)(CHCl₃): 2120, 1795, 1740 cm⁻ ¹.

EXAMPLE 17 Benzyl 6α-benzyl-6β-aminopenicillanate

A solution of benzyl 6α-benzyl6β-isocyanopenicillanate (1.75 g) inchloroform (50 ml) was stirred with p-toluene sulphonic acid (0.83 g)for 1/2 hour at 20°.

The chloroform was washed with aq. sodium bicarbonate dried andevaporated to give the essentially pure amine (100%). Chromatographyover silica gel provided the pure amine, m.p. 99°-101°ν_(max) (CHCl₃):3360, 1775, 1750 cm⁻ ¹. Alternatively addition of p-toluene sulphonicacid to the crude amine dissolved in ether provided the p-toluenesulphonic acid salt m.p. 163°-164°.

EXAMPLE 18 Benzyl 6α-(benzyloxycarbonylethyl)-6β-aminopenicillanate

Following the procedure of Example 17 benzyl6α-benzylcarbonylethyl-6β-isocyanopenicillanate (2.54 g) provided thetitle compound as a syrup. ν_(max) (CHCl₃) 3350, 1770, 1740, 1600 cm⁻ ¹.

EXAMPLE 19 Benzyl 6α-(methylthio)-6β-aminopenicillanate

Benzyl 6α-methylthio-6β-isocyanopenicillanate (3.61 g) was dissolved inchloroform (110 mls) and treated with p-toluene sulphonic acid (1.9 g).After 80 mins at 5° the solution was washed with aq sodium bicarbonate,dried and evaporated. A solution of the residual free base in ether (150mls) on treatment with p-toluene sulphonic acid provided withcrystalline p-toluene sulphonic acid salt (56%, m.p. 136°-138° dec).

ν_(max) (CHCl₃): 3200-3300 (b), 1785, 1740 cm⁻ ¹.

Phenylacetylation of benzyl 6α-(methylthio)-6β-aminopenicillanate usingphenylacetyl chloride, followed by the chlorine-trithylamine-methanolprocedure of Spitzer and Goodson (Tetrahedon Letters, [1973] 273)produced benzyl 6α-methoxy phenylacetamido penicillanate which wasconverted to 6α-methoxy phenyl-a acetamidopenicillanic acid by catalytichydrogenation.

We claim:
 1. A process for the conversion of a compound of the formula: ##STR8## wherein n is zero or 1, X is COOH, a non-toxic salt thereof or a conventional penicillin ester, and R' is hydroxyalkyl, alkoxycarbonylalkyl, aralkoxycarbonyl-alkyl, aralkyl or alkylthio into a compound of the formula: ##STR9## which comprises reacting a compound of the formula (VII) with an acid capable of converting CN to NH₂ and which does not cleave the β-lactam ring of the penam.
 2. A process according to claim 1 wherein n is zero.
 3. A process according to claim 1 wherein X is a conventional penicillin carboxylic acid ester.
 4. A process according to claim 3 wherein X is a benzyl, phthalidyl or t-butyl ester.
 5. A process according to claim 1 wherein the acid is an arylsulphonic acid.
 6. A process according to claim 5 wherein the arylsulphonic acid is p-toluenesulphonic acid.
 7. A process according to claim 1 wherein R' is methoxy.
 8. A process according to claim 1 wherein R' is alkylthio. 